1. Field of the Invention
The present invention relates to improved anti-paralleling apparatus for high-voltage switchgear and, more particularly, to improved apparatus in high-voltage switchgear for preventing simultaneous closure of two switches, which apparatus is simple and inexpensive to fabricate and associate with the switches, exhibits improved operation, and requires little space. The anti-paralleling apparatus of the present invention is an alternative to the apparatus described and claimed in commonly-assigned, co-pending U.S. patent application, Ser. No. 201,684, filed Oct. 29, 1980. The apparatus of the present invention is especially useful with switchgear containing two switches which are mounted in a so-called back-to-back configuration, as shown in commonly-assigned, co-pending U.S. patent application Ser. No. 136,632, filed Apr. 1, 1980. The anti-paralleling apparatus of application Ser. No. 201,684 is more conveniently used in high-voltage switchgear having two switches mounted side-by-side.
2. Background of the Invention
A wide variety of high-voltage switchgear is available. Such switchgear often contains first and second three-phase switches. Each switch may be in series with a respective alternating high-voltage power source, one of which may be used as a preferred power source, the other of which may be used as an alternate power source. The switches may be connected to a common bus within the switchgear. The common bus is connected to loads or other downstream devices intended to be powered by one of the sources. Normally, the first switch, in series with the preferred power source, is closed to energize the loads connected to the bus, while the second switch, in series with the alternate power source, is open. Should the preferred power source experience an interruption in service, or should it become otherwise necessary or desirable to connect the alternate power source to the loads, the normally closed first switch is opened and the normally open second switch is closed. These switch operations--opening or closing--may be effected by manual or motorized operating mechanisms. The latter may be automatically responsive to the condition and availability of the power sources and may be remotely operable.
Usually, the preferred and alternate power sources are totally separate and are not electrically associated. This, of course, assures that even if one of the sources experiences difficulty, there is a high probability that the other source is available for powering the loads connected to the common bus. However, the separation and disassociation of the sources also leads to their being electrically dissimilar at any given instant in time. In brief, the preferred and alternate sources are electrically out of phase. For this reason, it is undesirable that both switches be simultaneously closed. Simultaneous closure of the switches parallels the sources via the common bus. Because the sources are out of phase, paralleling them will effect current flow therebetween, an undesirable condition which can damage the sources, the gear, the loads, or the interconnections thereamong.
An overall object of the present invention, then, is the provision of improved apparatus which prevents the simultaneous closure of two separate switches in high-voltage switchgear. Specifically, this apparatus should positively prevent one switch from closing if the other switch is closed. The apparatus should also prevent the switches from closing at the same time.
Anti-paralleling apparatus of the various configurations and types are known in the art. Many are expensive or difficult to fabricate or to associate with the switches. Others are unreliable in operation, are quite complicated, or require substantial amounts of room within the switchgear. Anti-paralleling apparatus which is wholly or primarily electrical in nature and which depends for proper operation on drawing power from the power sources, is often deemed undesirable. Such undesirability arises from the possibility that one or both sources may become inoperative or unavailable while the need or desire to prevent simultaneous switch closure remains. Anti-paralleling apparatus which is electrical may alternatively be powered by a local power source, such as a local battery. Proper operation of the apparatus, therefore, depends on the availability and integrity of the local power source, which may be difficult to ensure.
Accordingly, a further object of the present invention is the provision of inexpensive, reliable totally mechanical anti-paralleling apparatus which does not depend on the presence of electrical power for proper functioning.
Other types of wholly mechanical anti-paralleling apparatus are known. Certain types of such anti-paralleling apparatus prevent simultaneous closure of the switches. However, if the first switch is closed when the second switch attempts to close (which it cannot because of the functioning of the anti-paralleling apparatus), the second switch may subsequently close in response to the first switch reopening. This occurrence is peculiar to switchgear having operating mechanisms which, once activated, continue to apply a closing force to their associated switches. The continuously applied force applied to the second switch is effective to close it immediately upon the first switch reopening. Electrically, this closure may not be deleterious to the power source, the switchgear, or the loads, because only one switch is closed. However, it may be desirable to prevent closure of the second switch whenever the second switch attempts to close while the first switch is closed and the second switch continues this attempt through the time the first switch reopens. Preventing closure of the second switch in this instance may be desirable until there has been some intervention following the reopening of the first switch. For example, a workman may approach the switchgear while the first switch is closed and the second switch is open; the workman may not know that the operating mechanism for the second switch is applying a continued closing force thereto. The workman may manually open the first switch not realizing that this has resulted in the second switch closing and in the common bus remaining energized. The workman's contact with the common bus or with items connected thereto--which he believes to be de-energized--could prove injurious to him.
Accordingly, yet another object of the present invention is the provision of anti-paralleling apparatus which positively prevents a closure of the second switch if the first switch is closed and which also prevents closure of the second switch after the first switch reopens if the operating mechanism for the second switch attempted to initiate closure thereof (which was initially prevented by the apparatus) and continues to attempt to initiate closure through the time the first switch reopens.